They only give second chance chests to certain bosses for two reasons.

RatbeardGenerally speaking, two things have to be true before we'll consider adding a Second Chance chest:

1) Is the boss in question at the end of a really long instance?

2) Does the boss in question have unique loot?

I don't know about the Snake Pit, but the Mooshu guardian bosses and the Ulysses palace dungeon doesn't take that long to complete. In fact, you don't have to face a mob fight in the Mooshu guardian dungeons.